Most of the movements of the joints and especially limbs of the human body are based on a structure in which a tubular bone is joined to another tubular bone via a so-called hinge joint. The movement resembles the action of a mechanical hinge and takes place mainly two-dimensionally about a pivot point with a constant radius. An example of such movement is that of the elbow joint. However, the action of a hinge joint is not quite as simple as this, but this is the basic principle.
The action of the spine is not as simple as this. The spinal column consists of vertebrae and disks between them. Adjacent vertebrae are joined together via the disk and so-called facet joints. Successive vertebrae and the disk between them are called a functional spine unit (FSU). The movements of the spine cannot be described on the principle of the hinge joint, but the FSU always works in a three-dimensional fashion, comprising both rotation and sliding in different directions of motion.
FIG. 1 presents a model of a pair of spinal vertebrae C1 and C1-1 with a three-dimensional xyz-coordinate system focused in the centre of the upper vertebra C1 in the pair of vertebrae. The x-direction here means the direction corresponding to the frontal direction of a person, i.e. the direction in which the front side of the body faces. The y-direction means a lateral direction which is horizontal and perpendicular to the x-direction. The z-direction means a vertical direction perpendicular to the xy-plane. It can be seen from FIG. 1 that there may be a total of 12 load components, linear and rotatory, acting via these axes. The application of a load to any one of the axes produces a displacement of the upper vertebra C1 relative to the lower vertebra C1-1. The displacement is the sum of rotation and sliding in the directions of motion.
As early as in the 1960""s it was established in experimental research that rotatory (axial rotation) and lateral effects in the FSU mechanism are interlinked; reference is made to a phenomenon called xe2x80x98coupling movement patternsxe2x80x99 (Soobey JR.: Motion testing of the cervical spine. J. Amer Oseopath Ass 1967; 66:381; Lysell E: Motion in the cervial spine. Acta Orthop Scan 1969; Suppl. 123:1; White AM and Panjabi M: The basic kinematics of the human spine 1978; 3:13 and White AM and Panjabi M: Clinical Biomechanics of the Spine. Lippincott, Philadelphia, 1978). This also means that, in spinal movements, lateral flexion and rotation tend to occur simultaneously. Accordingly, in free spinal movements there appears no single-plane motion or motion about a single fulcrum. In movements in the lower part of the spine, deviations between two-dimensional and natural motion are smaller than in the cervical spine, where combined movement patterns are ostensibly significant.
In FIG. 2, a person is depicted diagrammatically in front view while FIG. 3 shows the same person in side view. In the figures, the sketch in heavier lines depicts a neutral position of the head, whereas the sketch in lighter lines shows the position of the head after rotation toward the left. FIGS. 2 and 3 illustrate the fact that rotation also involves simultaneous sideways tilting of the head in the direction of the rotation as well as an inclination forward. Thus, the cervical spine follows a three-dimensional pattern of motion.
In prior art, a rotation exercise apparatus is known which comprises an equipment frame, a turning arbor mounted on the equipment frame so as to permit rotation about a vertical axis, and a head rest element designed to hold the head and connected to the turning arbor.
A problem with the prior-art apparatus is that it only implements an exclusively linear or two-dimensional movement pattern, which means that the motion of the cervical spine does not follow a natural path. As stated above, the cervical spine in fact follows a three-dimensional movement pattern. Therefore, when head rotation exercises are done using this prior-art apparatus, an incorrect movement pattern is learned and the incorrectly applied stress may involve a risk of injury.
The object of the present invention is to eliminate the above-mentioned drawbacks. A specific object of the present invention is to disclose an apparatus having a head rest element that implements a natural three-dimensional motional pattern so that a correct three-dimensional path of the cervical spine can be learned using the apparatus and that the apparatus allows exercise and rehabilitation of the muscles moving the cervical spine in a way permitting correct application of stress to them.
According to the invention, the head rest element comprises means for holding the head of the person performing an exercising movement substantially immobile on the head rest element. The apparatus comprises a turning device connecting the head rest element to a turning arbor. The turning device allows simultaneous turning of the head rest element about three axes perpendicular to each other. Moreover, the apparatus comprises a control gear which controls the turning of the head rest element connected to the turning device as a function of the angle of rotation of the turning arbor so that the head rest element turns simultaneously about said axes in predetermined proportions corresponding to the natural three-dimensional motional pattern of head rotation.
When the head rest element is rotated about its vertical axis, the turning device allows a three-dimensional path for the head rest element so that simultaneous rotation about three axes perpendicular to each other takes place. When these motional degrees of freedom are interlinked by the control gear so that they occur in predetermined proportions to each other, the head rest element is caused to implement a three-dimensional motional pattern with rotation accompanied by lateral and forward inclination of the head. Thus, the invention has the advantage that the apparatus allows the exercise of movements along the natural three-dimensional path. The exercise can be performed with or without load. The advantages of a load on movements following the natural path are the following: During exercise, stress is correctly applied to those tissues to which it is intended to be applied. Furthermore, correct motional patterns are learned. This means that the motional patterns learned during exercises and rehabilitation are very likely to be correctly applied outside the exercise or rehabilitation situation as well. In addition, the risk of injury due to incorrect application of stress during exercise and rehabilitation is reduced.
In an embodiment of the apparatus, the apparatus comprises a seat provided with a back rest, holding means for holding a person""s torson against the back rest, and adjusting elements for the adjustment of the position of the seat in relation to the equipment frame. Using the adjusting elements of the seat, a person can be individually seated in an accurate position relative to the equipment frame and the turning mechanism. In practice, the head rest element is at a certain height from the floor level, and in order to fit the head of the person sitting on the seat to the head rest element, the position and height of the seat are adjusted so that the head can be held by the head rest element.
In an embodiment of the apparatus, the head rest element is a helmet or the like which is capable of supporting the head from all sides. Therefore, the helmet has an interior space for receiving the head into it.
In an embodiment of the apparatus, the turning device comprises a first frame, which is attached to the turning arbor so that it turns with the turning arbor about a vertical first swing axis parallel to the z-axis. It is assumed that an xyz coordinate system is so attached to the turning arbor that the z-axis coincides with the first swing axis that the xy-plane turns with the turning arbor. Furthermore, the turning device comprises a second frame, which is pivotally mounted on the first frame so that it turns about a second swing axis parallel to the x-axis. In addition, the apparatus comprises a third frame, which is pivotally mounted on the second frame so that it turns about a third swing axis parallel to the y-axis, said third swing axis being disposed near the second swing axis perpendicularly to it. The head rest element is attached to the third frame. Thus, the head rest element can simultaneously turn about the vertical first swing axis, tilt sideways and perform a forward inclination.
In an embodiment of the apparatus, the first frame is arranged to extend downward and backward from the turning arbor to a point behind the head rest element so that it extends behind the neck of the person having his/her head in the head rest element. The second frame is pivotally mounted on said part of the first frame extending behind the head rest element, so that the second swing axis lies in the vertical centre plane of symmetry of the head rest element.
In an embodiment of the apparatus, the control gear comprises a first set of transmission elements for turning the second frame about the second swing axis parallel to the x-axis in relation to the first frame with a predetermined first transmission ratio when the turning arbor is turning about the first swing axis parallel to the z-axis.
In an embodiment of the apparatus, the control gear comprises a second set of transmission elements for turning the third frame about the third swing axis parallel to the y-axis with a predetermined second transmission ratio when the turning arbor is turning about the first swing axis parallel to the z-axis.
In an embodiment of the apparatus, the first set of transmission elements comprises a first turning element, e.g. a wheel or the like, which is attached to the turning arbor. A second transmission element, e.g. a wheel or the like, is attached to the second frame. A flexible elongated draw element is attached to the first and second turning elements to transmit the rotary motion of the turning arbor so as to turn the second frame with respect to the first frame.
In an embodiment of the apparatus, the second set of transmission elements comprises a projection attached to the turning arbor and extending in a substantially transverse direction from the turning arbor. A rocking arm is pivotally connected via a joint in its mid portion to the projection so that it can turn about a horizontal axis. The rocking arm comprises a front end, which is on the front side of the joint, and a rear end, which is on the rear side of the joint. Furthermore, the second set of transmission elements comprises a first rod, whose lower end is connected via a joint to the third frame and/or to the head rest element and whose upper end is connected via a joint to the rear end of the rocking arm. Moreover, the second set of transmission elements comprises a second rod, whose lower end is connected via a joint to the front end of the rocking arm and whose upper end is connected via a joint to the equipment frame.
In an embodiment of the apparatus, the first rod is connected to the third frame and/or head rest element and to the rocking arm via ball joints. The second rod is connected to the rocking arm and equipment frame via ball joints.
In an embodiment of the apparatus, the apparatus comprises a resistance means for producing a force opposing the rotation exercise movement.
In an embodiment of the apparatus, the resistance means is connected to the turning arbor to generate a torque opposing the rotation of the turning arbor.
In an embodiment of the apparatus, the resistance means works on the principle of gravitational resistance. The resistance means comprises a counterweight, which consists of a number of individual weight elements which can be combined to produce a predetermined load.
In an embodiment of the apparatus, the resistance means comprise a third wheel, which is connected to the turning arbor, and a flexible elongated second draw element for transmitting the load of the counterweight to the third wheel.
In an embodiment of the apparatus, the resistance means comprises an eccentric gear arranged to act between the second draw element and the counterweight so that a load opposing the exercise movement with a force varying in a predetermined manner as a function of the rotational angle of the turning arbor is created.
In an embodiment of the apparatus, the apparatus comprises adjustable limit stops for adjustment of the permitted range of exercise movement.